Process of hardening copper containing steels for structural and similar purposes



Patented Dec. 8, 1931 UNITED STATES.

PATENT OFFICE FRANZ NEH'I', OF HUM-3m, GERMANY, ASSIGNOB TO THE FIRM VEREINIGTE ST'AHLWEBKE AKTIENGESELLSGHAIT, OF DUSSIEEDORF, GERMANY OF EARDENING OOPPER- CONTAINING STEELS FOR STRUCTURAL AND SIMILAR PURPOSES No Drawing. Application filed April 5, 1929, Serial No. 352,918, and in Germany April 5, 1928.

In order to obtain in the ordinary steels for structural and similar purposes a ratio between the elastic limit and the tensile strength of more than 70%, such steels had up to now of the steel to above the upper change-point (A0 point), whereupon the steel was allowed to cool from a temperature above the saidpoint and tempered to a temperature below the A0 change-point.

In carrying out such heat treatment, it has been proposed to treat an alloy steel containing approximately .05% up to 5% of copper by subjecting the steel after it has been cast into ingots or worked into finished parts to normalizing treatment by heating it to a relatively high temperature, for example, 845 C. for a time suflicient to ensure the entire mass reaching the said temperature and by'maintaining the said temperature for a relatively short period and then allowing the steel to cool slowly, preferably in air, such treatment being followed by a reheating treatment to a temperature of between 510 and 550 C. atwhich temperature the steel is maintained for a relatively short time before being again cooled. The result of this two-stage heat treatment is a change in the physical properties of the steel which shows increases in the yield point, ultimate strength, elongation, reduction of area and the Brinell hardness.

The object of the present invention is to provide a process according to which a h'ardening of a copper-containing steel may be obtained by only tempering the steel, thus doing away with any additional heating. It will be understood that such a process ofiers considerable economical advantages in the production of structural and other elements of construction by casting, rolling or forgmg.

The process is based upon the discovery that in steels having a copper content of more than 0.6% but not more than about 10% and a carbon content of up to 0.5%, a hardening effect may be produced by tempering at a temperature below the A0, point until the elastic limit as well as the tensile strength is increased, whereas the elongation, contraction and notch-bar toughness is decreased, the increase in the elastic limit being greater than that in tensile strength so that the ratio elastic limit to tensile strength will thus be raised to about 7 0 to 80%.

According to the presentinvention .the saidsteel is subjected to a single heat treatment by maintaining it for at least an hour at a temperature below the A0 point, until an increase in the elastic limit and the tensile strength is secured, accompanied by a decrease in the elongation, contraction and notch-bar toughness.

According to the invention, moreover, in circumstances where the decrease in notch.- bar toughness is undesired, this may be avoided by subjecting the steel to the final shaping operations at a temperature range of 900 to 800 C. before it is subjected to the single heat treatment hereinbefore referred The tempering temperature which is best suited for the purpose of the invention depends upon the chemical composition, yet Will always lie below the A0 change point (the lower limit being about 400 (1.). It

may be necessary to determine the most suitable temperature for any particular steel by experiment. In order to obtain the maximum increase in tensile strength a tempering period of atleast sixty minutes duration is required. If desired, the steel may be air cooled.

The new process makes it possible to increase the elastic limit of the copper steel by more than 50% and the tensile strength by more than 20%. The marked decrease in notch-bar toughness, which in some cases would prevent the commercial application of the process, may as hereinbefore stated, be successfully avoided by effecting the final shaping operation whether eifected by rolling or orging at a temperature range of 900 to 800 (3., whereupon the workpiece, after having been air-cooled, will be tempered in the described way.

The following example is given for the purpose of making the advantages of the process better understood. The material employed wasofthe following composition:

Per cent C 0. 08 P 0. 017 Si 0. 05 Mn i. '0- S -J; 0. 014 Cu -i 1. 01

The cast ingot was rolled down into a bar of 118 x 8 inch. The following physical properties were obtained:

Rolled Rolled under Finishing under normal conrolling temp. normal ditlons, air 820 0., conditions, cooled temair-cooled,

r pered at tempered at cooled 600 C. 600 C. I Elastic 1lmit 37036 65274 655581bs./sq. in. Tensile strength 62017 81734 84004 Elongation 22. 6% 15. 6% 17. 5% Contraction 60% 57% 60. 05% Notch-bar toughness 326 57 318 lbs/sq. in.

The steel was maintained at the temperature of 600 C. for a period exceeding one hour. It may be mentioned that by quenching, according to known processes, in water at 980 C. an elastic limit of only 53212 lbs/sq. in. and a tensile strength of 65274 lbs/sq. in. had been obtained.

Having thus described the invention, what Iclaim as new and desire to secure by Letters Patent is:

1. Process for improving the physical properties of copper containing steels for structural or similar purposes, which consists in subjecting a steel having a copper content of more than 0.6% but no more than about 10% and a carbon content of upto 0.5% to a single heat treatment by maintainmg it for at least an hour at a temperature below the A0 point until a substantially maximum increase in the elastic limit and in the-tensile strength is obtained while at the same time a decrease in the elongation, contraction and notch-bar toughness is secured.

2. A steel having a copper content of more than 0.6% but less than 10% and a carbon content of up to 0.5%, which has been subjected to a single heat treatment by being tempered for at least an hour at a temperature below the Ac point until it acquires a substantiallv maximum increase in its elastic limit and its tensile strength and at the same time a decrease in its elongation, its contraction and its notch-bar toughness.

FRANZ NEHL. 

